1. Technical Field
The present invention relates to a common mode filter and a method of manufacturing the same, and more particularly relates to a multilayer common mode filter and a method of manufacturing the same.
2. Background
Common mode noise describes the type of noise that is conducted on all lines in the same direction. To suppress common mode noise, common mode filters or chokes can be installed on conducting lines where common mode noise is present. Traditionally, a common mode filter is comprised of components including an iron core and two coils wound around the iron core with the same winding number. When common mode current flows through the common mode filter, the two coils generate magnetic flux in the same direction such that the common mode filter exhibits high impedance and can suppress common mode noise.
To address the requirement of portable electronic apparatuses, thin film common mode filters have been developed. Japanese Patent Application No. JP2000173824 (A) discloses a thin film common mode filter. The thin film common mode filter has an upper magnetic layer, a lower magnetic layer, a plurality of insulative layers and a plurality of conductive patterns. The plurality of insulative layers and the plurality of conductive patterns are alternatively formed between the upper and lower magnetic layers.
Furthermore, U.S. Pat. No. 7,145,427 B2 discloses one type of thin film common mode filter, which includes two coil conductor layers, two lead-out electrode layers, a plurality of insulation layers, and two magnetic layers. Each coil conductor layer includes a coil, and the two lead-out electrode layers are used to extend the inner ends of the two coils to an edge of the thin film common mode filter for achieving an external electrical connection. The insulation layers are used for electrically insulating the coil conductor layers and the lead-out electrode layers. The coil conductor layers, the lead-out electrode layers, and the insulation layers are disposed between two magnetic layers.
Limited by dimensions, higher common mode impedance or different cut off frequencies cannot be easily obtained by modifying the coil structure of the above-mentioned thin film common mode filter. If the increase of the common mode impedance is achieved by adding to the number of windings, more space will be needed to install the thin film common mode filter, creating an adverse effect on the application of the thin-film common mode filter to portable electronic products.